The pro Remain wing of the Labour Party, which is dominant in its parliamentary party and in much of its traditional establishment, won a huge internal victory yesterday.
The overwhelming conference vote to keep open the option of a fresh Brexit vote was seized upon by Keir Starmer in his speech, in which he made clear that Labour would probably vote against any deal reached by Theresa May. He also made clear that staying in the EU was an option.
This is a massive moment in British politics, which puts Brexit in jeopardy. But it is also a huge risk for the Labour Party, which has been all over the place since the June 2016 UK vote to leave the European Union.
Jeremy Corbyn and many of his supporters are eurosceptics and have been since the days that key Labour figures joined up with nationalist Tories such as Enoch Powell to oppose entry into the European Economic Community in 1973.
Last year Labour fought the general election on a platform to implement Brexit, but since the unexpectedly narrow result Mr Corbyn’s objective has been to topple the government.
This is not surprising in an opposition party that is on the brink of power but yesterday’s conference decision shows that Labour’s concerns about Brexit are not entirely ideological, like those of the Liberal Democrats, but opportunistic.
Now more than ever the prime minister is going to struggle to get anything at all on Brexit through the House of Commons. The EU more than ever is emboldened to offer the UK as little as possible.
A general election might be the only way out of this mess.
The risk for Labour is that pro Brexit activists rally round pro Brexit candidates in every constituency, putting at risk once safe Labour seats.
This might all work for Labour or it might be a boost to the Tories, ultimately leading to a hard Brexit, but further political chaos for the country is now almost certain.